There are known a number of fire and explosion detection systems employing UV and IR detectors in combination. Examples of such systems are illustrated in the following U.S. Pat. Nos. 3,665,440; 3,653,016. The apparatus described in U.S. Pat. No. 3,665,440 provides an alarm output when IR is detected in the absence of UV. The apparatus described in U.S. Pat. No. 3,653,016 provides an alarm output when IR and UV are detected together but also includes a portion of the visible spectrum in the detection ranges of the detectors.
U.S. Pat. No. 4,270,613 of the present applicant/assignee describes a particularly useful detection system which provides an output indication in response to coincident detection of UV and IR wherein the detection bands exclude the visible spectrum.